The present invention is, in general, directed to an electrochemical device, and to a process for making an electrochemical device having a carboranyl magnesium electrolyte, and in particular to an electrochemical device having a carboranyl magnesium electrolyte which is compatible with a magnesium anode and a cathode made of a non-noble metal while maintaining an oxidative stability>3.0V vs. a magnesium reference.
Due to the formation of an ion blocking layer at the electrode surface, most common salts of magnesium (Mg) cannot be used as effective magnesium battery electrolytes. It has been shown previously that Grignard reagents (R—Mg—X) support magnesium deposition and stripping. Currently, typical electrolytes are based on a group of compounds known as organohaloaluminates which are obtained by the reaction of an alkyl Grignard or aryl Grignard with an aluminum based Lewis Acid (AlX3). Other non-haloaluminate electrolytes compatible with Mg metal with high reported stability are based on tris(3,5-dimethylphenyl)borane and phenyl Grignard.
The above compounds have been shown to effectively mediate reversible magnesium deposition and stripping with enhanced current density as compared to previously assessed electrolytes, but are incompatible with non-noble metal electrodes such as stainless steel, copper, and aluminum. For example, these compounds have been shown to be stable to >3.0 V (vs. magnesium reference) at a platinum surface but were found to have a much lower stability on stainless steel, i.e. <2.5 V (vs. magnesium reference) and <2.0V on aluminum (vs. magnesium reference), due to their incompatibility with these metal surfaces at potentials >2.5 V (vs. magnesium reference). This prevents the use of non-noble metals as current collectors in contact with the high voltage cathodes thereby limiting the energy density of a theoretical magnesium battery. Additionally, a theoretical magnesium battery in which a noble metal is used as current collectors would incur very high costs.
Accordingly, there exists a need for an improved electrolyte which would be compatible with non-noble metal electrodes.